          Lecture 4 - Page 10 : 34
 Functional Programming in SchemeHigher-order Functions * Introduction to higher-order functions Higher-order functions Some simple and general higher-order functions Linear search in lists Generation of list selectors * Mapping and filtering Classical higher-order functions: Overview Mapping The mapping function Examples of mapping Filtering The filtering function Examples of filtering * Reduction and zipping Reduction The reduction functions Accumulation Zipping The zipping function * Currying The idea of currying Currying in Scheme Examples of currying Ad hoc currying in Scheme (1) Ad hoc currying in Scheme (2) * Web related higher-order functions HTML mirror generation HTML mirror usage examples Making tables with the real mirror Tables with higher-order functions HTML element modifications The function simple-html-table The XHTML mirror in LAML Generation of a leq predicate from enumeration
 Examples of mapping We will now study a number of examples.
 Expresion Value ```(map string? (list 1 'en "en" 2 'to "to"))``` `(#f #f #t #f #f #t)` ```(map (lambda (x) (* 2 x)) (list 10 20 30 40))``` `(20 40 60 80)` ```(ul (map (compose li (compose b (lambda (x) (font-color red x)))) (list "a" "b" "c") ) )``` a b c Same as above ```
• a
• b
• c
```

In the first row we map the string? predicate on a list of atoms (number, symbols, and strings). This reveals (in terms of boolean values) which of the elements that are strings. In the second row of the table, we map a 'multiply with 2' function on a list of numbers. The third row is more interesting. Here we map the composition of li , b , and red font coloring on the elements a, b, and c. When passed to the HTML mirror function ul , this makes an unordered list with red and bold items. Notice that the compose function used in the example is a higher-order function that can compose two or more functions. The function compose from lib/general.scm is such a function. Notice also that the HTML mirror function ul receives a list, not a string. The fifth and final row illustrates the raw HTML output, instead of the nicer rendering of the unordered list, which we used in the third row.